The staining of biological cells and tissues with dyes, especially fluorescent dyes, in order to render them more observable or to differentiate types of cells, is well known in the art. There is a continuing need to find more efficient means of staining.
Further, chemical analysis of liquids, such as water, milk and biological fluids is often desirable or necessary for health maintenance and diagnostic care. Various compositions and elements to facilitate such analyses are known. Such compositions and elements generally include a reagent composition for determining a substance under analysis, identified as an "analyte" herein. The analyte can be a living organism, such as a bacterium or a yeast cell, or a nonliving chemical substance. The reagent composition, upon interaction with the analyte, provides a detectable change (e.g. dye formation).
Recently, much work has been directed to developing compositions and elements which are useful for rapid and highly quantitative diagnostic or clinical analysis of biological fluids such as whole blood, blood sera, plasma, urine and the like.
For example, for the rapid and effective diagnosis and treatment of infectious diseases, it is desirable to be able to detect the bacteria causing the disease as rapidly as possible. Infections of the urinary tract are among the most common bacterial diseases, second in frequency only to infections of the respiratory tract. Most urinary tract infections are associated with bacterial counts of 100,000 or more organisms per ml of urine, a condition referred to as significant bacteriuria.
In U.S. Ser. No. 824,766 of Belly et al noted above, novel reducible compounds are described and claimed which are useful in the detection of bacteria as well as other analytes. The compounds and assays described in this application can be used to determine an analyte, e.g. a bacterium, which reduces a reducible compound thereby releasing a detectable species, e.g. a colored or fluorescent dye, at a pH of 9 or less.
In U.S. Ser. No. 824,757 of Babb et al noted above, certain reducible compounds are described which are useful for releasing phenalenone and benzphenalenone fluorescent dyes. These dyes can be used to stain biological specimens and to determine an analyte, such as a bacterium.
While those assays represent significant advances in the art, it would be desirable to improve the sensitivity of the assays even further in order to extend their usefulness to determine analytes at much lower concentrations.